In high-voltage, direct current (HVDC) electric power transmission systems direct current (DC) is used for the bulk transmission of electrical power, in contrast with the more common alternating current systems. A flexible alternating current transmission system (FACTS) is a system composed of static equipment used for alternating current (AC) transmission of electrical energy. FACTS is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics-based system.
An arc fault may generally be described as a high power discharge of electricity between two or more conductors. This discharge usually translates into heat, which can break down the conducting wire's insulation and possibly trigger an electrical fire. These arc faults can range in current from a few amps up to hundreds of thousands of amps high and are highly variable in terms of strength and duration. Common causes of arc faults include faulty connections due to corrosion faulty initial installation, and semiconductor failures in the converter. In the improbable case of an internal fault (fault arc or arc fault) in any of the above described systems, installation safety and personal safety must be ensured.
In the context of power electronics converter systems used in motor drive industries, HVDC and FACTS, modular converter cells are applied as building blocks of power converter systems. Modular converter systems usually have multiple redundant power cells for a reliable operation of the system. Therefore, when one cell fails during fault, the entire converter system should be able to continue operating until the next scheduled maintenance. To ensure the continued converter operation without breakdown, the faulty cells should be bypassed inter alia by means of electrically connecting two busbars with very fast speed. During healthy condition, the two busbar terminals should be properly insulated to avoid any accidental short-circuit fault.
In the present design of semiconductor modules for HVDC electric power transmission systems and FACTS, failures are handled by an internal short circuit mode. Future constructions may need external (“bypass”) short-circuit modes to handle certain failure situations.
In some arc-quenching bypass switches, additional insulation layers or membranes are used to provide extra separation between two busbar contacts. The insulation layers are typically made of ceramics or general-purpose thermal plastics.